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LetusXL DoF Adapter Help and Questions


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#1 Ron Flex

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Posted 16 June 2009 - 01:31 PM

Hello, I recently bought a LetusXL adapter for my XL2. It has not arrived yet. I am completely confused about the issues of flange focal distance and back focus with this adapter.

It comes with a Nikon mount but the lenses are expensive and I already own a lot of FD lenses. I bought a glassless adapter that allows an FD lens to mount to a Nikon body. I assumed issues regarding infinity focus did not matter when it came to these adapters.

I knew there would be some issues regarding flange focal diastance however I assumed the back focus lens that mounts to the XL body would rectify this problem. I thought this was its use.

I have been told that the back focus will allow FD lenses to focus infinity (or near enough) and others have said that the back focus will have no effect. What is the real deal here? A few of these LetusXL adapters even had reversible mounts for both FD and Nikon!!

Also will I be able to mount a 50mm F2 Pre-AI Nikkor to the mounts that Letus use?

Thanks!
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#2 Chris Keth

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Posted 16 June 2009 - 02:34 PM

Hello, I recently bought a LetusXL adapter for my XL2. It has not arrived yet. I am completely confused about the issues of flange focal distance and back focus with this adapter.

It comes with a Nikon mount but the lenses are expensive and I already own a lot of FD lenses. I bought a glassless adapter that allows an FD lens to mount to a Nikon body. I assumed issues regarding infinity focus did not matter when it came to these adapters.

I knew there would be some issues regarding flange focal diastance however I assumed the back focus lens that mounts to the XL body would rectify this problem. I thought this was its use.

I have been told that the back focus will allow FD lenses to focus infinity (or near enough) and others have said that the back focus will have no effect. What is the real deal here? A few of these LetusXL adapters even had reversible mounts for both FD and Nikon!!

Also will I be able to mount a 50mm F2 Pre-AI Nikkor to the mounts that Letus use?

Thanks!


Whatever mount you use, it must be set to the proper and exact (we're talking thousandths of a millimeter precision) flange focal depth. Period. If it's not, your focus markings will be off and your close focus distance or your infinity focus will be affected (which of those depends on which way it is off, long or short)
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#3 Ron Flex

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Posted 16 June 2009 - 02:39 PM

Whatever mount you use, it must be set to the proper and exact (we're talking thousandths of a millimeter precision) flange focal depth. Period. If it's not, your focus markings will be off and your close focus distance or your infinity focus will be affected (which of those depends on which way it is off, long or short)


And will the back focus lens be able to rectify this to some degree?
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#4 Chris Keth

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Posted 16 June 2009 - 03:26 PM

And will the back focus lens be able to rectify this to some degree?


I'm not sure what you mean by backfocus lens. Do you mean the diopter that goes in between the camera and the letus?
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#5 Ron Flex

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Posted 16 June 2009 - 03:33 PM

I'm not sure what you mean by backfocus lens. Do you mean the diopter that goes in between the camera and the letus?


Yes, it is the modified Minolta lens at the rear of the unit which attached to the Letus. It acts as a relay lens and has backfocus adjustment. Image is here:

Posted Image
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#6 Chris Keth

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Posted 16 June 2009 - 03:39 PM

The backfocus of that lens will correct the backfocus on the sensor of your camera. That is completely unrelated to the flange focal depth of the letus itself. Adjusting one will do nothing to correct the other.
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#7 Ron Flex

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Posted 16 June 2009 - 04:16 PM

The backfocus of that lens will correct the backfocus on the sensor of your camera. That is completely unrelated to the flange focal depth of the letus itself. Adjusting one will do nothing to correct the other.


Thanks for clearing that up.

I guess the lack of infinity focus is not the worst thing for a a DOF adapter as the whole point of it is to have a shallow DOF without having to zoom in the 20x lens.

Just depends on how much the infinity focus is afffected and to what affect it has on rack focusing. I have been looking at Nikon lenses but the prices are quite expensive.

The difference in price between a Canon FD 1.8 50mm and the same spec Nikkor is huge.

Edited by Ron Flex, 16 June 2009 - 04:21 PM.

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#8 Chris Keth

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Posted 16 June 2009 - 04:38 PM

Thanks for clearing that up.

I guess the lack of infinity focus is not the worst thing for a a DOF adapter as the whole point of it is to have a shallow DOF without having to zoom in the 20x lens.

Just depends on how much the infinity focus is afffected and to what affect it has on rack focusing. I have been looking at Nikon lenses but the prices are quite expensive.

The difference in price between a Canon FD 1.8 50mm and the same spec Nikkor is huge.


Well, yeah, it is a big deal. Potentially you could not be able to focus infinity at all. That is a problem. Also, focus marks being off pretty much makes the focus puller's life miserable.
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